﻿//===================================================================================
// Microsoft patterns & practices
// Composite Application Guidance for Windows Presentation Foundation and Silverlight
//===================================================================================
// Copyright (c) Microsoft Corporation.  All rights reserved.
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY
// OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT
// LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// FITNESS FOR A PARTICULAR PURPOSE.
//===================================================================================
// The example companies, organizations, products, domain names,
// e-mail addresses, logos, people, places, and events depicted
// herein are fictitious.  No association with any real company,
// organization, product, domain name, email address, logo, person,
// places, or events is intended or should be inferred.
//===================================================================================
using System;
using System.Reflection;

namespace Carcass.Events
{
  /// <summary>
  /// Represents a reference to a <see cref="Delegate"/> that may contain a
  /// <see cref="WeakReference"/> to the target. This class is used
  /// internally by the Composite Application Library.
  /// </summary>
  public class DelegateReference : IDelegateReference
  {
    private readonly Delegate _delegate;
    private readonly WeakReference _weakReference;
    private readonly MethodInfo _method;
    private readonly Type _delegateType;

    /// <summary>
    /// Initializes a new instance of <see cref="DelegateReference"/>.
    /// </summary>
    /// <param name="delegate">The original <see cref="Delegate"/> to create a reference for.</param>
    /// <param name="keepReferenceAlive">If <see langword="false" /> the class will create a weak reference to the delegate, allowing it to be garbage collected. Otherwise it will keep a strong reference to the target.</param>
    /// <exception cref="ArgumentNullException">If the passed <paramref name="delegate"/> is not assignable to <see cref="Delegate"/>.</exception>
    public DelegateReference(Delegate @delegate, bool keepReferenceAlive)
    {
      if (@delegate == null)
        throw new ArgumentNullException("delegate");

      if (keepReferenceAlive)
      {
        this._delegate = @delegate;
      }
      else
      {
        _weakReference = new WeakReference(@delegate.Target);
        _method = @delegate.Method;
        _delegateType = @delegate.GetType();
      }
    }

    /// <summary>
    /// Gets the <see cref="Delegate" /> (the target) referenced by the current <see cref="DelegateReference"/> object.
    /// </summary>
    /// <value><see langword="null"/> if the object referenced by the current <see cref="DelegateReference"/> object has been garbage collected; otherwise, a reference to the <see cref="Delegate"/> referenced by the current <see cref="DelegateReference"/> object.</value>
    public Delegate Target
    {
      get
      {
        if (_delegate != null)
        {
          return _delegate;
        }
        else
        {
          return TryGetDelegate();
        }
      }
    }

    private Delegate TryGetDelegate()
    {
      if (_method.IsStatic)
      {
        return Delegate.CreateDelegate(_delegateType, null, _method);
      }
      object target = _weakReference.Target;
      if (target != null)
      {
        return Delegate.CreateDelegate(_delegateType, target, _method);
      }
      return null;
    }
  }
}
